Process for tin/silicon coupling functionalized rubbers

ABSTRACT

Rubbery polymers made by anionic polymerization can be coupled with both tin halides and silicon halides to improve the characteristics of the rubber for use in some applications, such as tire treads. In cases where the rubbery polymer is synthesized by anionic polymerization utilizing a polar modifier it is difficult to attain a high level of coupling. This invention is based upon the unexpected finding that the coupling efficiency of rubbery polymers made with polar modifiers can be significantly improved by initiating the anionic polymerization with an alkylsilyloxy protected functional lithium initiator having a structural formula selected from the group consisting of: (a):  
                 
 
     wherein X represents a group IVa element selected from the group consisting of carbon, silicon, germanium, and tin, wherein Y represents phosphorous or nitrogen, wherein R represents alkyl groups that can be the same or different, wherein the alkyl groups contain from 1 to about 8 carbon atoms, and wherein A represents an alkylene group containing from 1 to about 12 carbon atoms.

BACKGROUND OF THE INVENTION

[0001] It is highly desirable for tires to exhibit good tractioncharacteristics on both dry and wet surfaces. However, it hastraditionally been very difficult to improve the tractioncharacteristics of a tire without compromising its rolling resistanceand tread wear. Low rolling resistance is important because good fueleconomy is virtually always an important consideration. Good tread wearis also an important consideration because it is generally the mostimportant factor that determines the life of the tire.

[0002] The traction, tread wear, and rolling resistance of a tire isdependent to a large extent on the dynamic viscoelastic properties ofthe elastomers utilized in making the tire tread. In order to reduce therolling resistance of a tire, rubbers having a high rebound havetraditionally been utilized in making the tire's tread. On the otherhand, in order to increase the wet skid resistance of a tire, rubbersthat undergo a large energy loss have generally been utilized in thetire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instancevarious mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubber material for automobile tire treads.However, such blends are not totally satisfactory for all purposes.

[0003] The inclusion of styrene-butadiene rubber (SBR) in tire treadformulations can significantly improve the traction characteristics oftires made therewith. However, styrene is a relatively expensive monomerand the inclusion of SBR is tire tread formulations leads to increasedcosts.

[0004] Carbon black is generally included in rubber compositions whichare employed in making tires and most other rubber articles. It isdesirable to attain the best possible dispersion of the carbon blackthroughout the rubber to attain optimized properties. It is also highlydesirable to improve the interaction between the carbon black and therubber. By improving the affinity of the rubber compound to the carbonblack, physical properties can be improved. Silica can also be includedin tire tread formulations to improve rolling resistance.

[0005] U.S. Pat. No. 4,843,120 discloses that tires having improvedperformance characteristics can be prepared by utilizing rubberypolymers having multiple glass transition temperatures as the treadrubber. These rubbery polymers having multiple glass transitiontemperatures exhibit a first glass transition temperature which iswithin the range of about −110° C. to −20° C. and exhibit a second glasstransition temperature which is within the range of about −50° C. to 0°C. According to U.S. Pat. No. 4,843,120, these polymers are made bypolymerizing at least one conjugated diolefin monomer in a firstreaction zone at a temperature and under conditions sufficient toproduce a first polymeric segment having a glass transition temperaturewhich is between −110° C. and −20° C. and subsequently continuing saidpolymerization in a second reaction zone at a temperature and underconditions sufficient to produce a second polymeric segment having aglass transition temperature which is between −20° C. and 20° C. Suchpolymerizations are normally catalyzed with an organolithium catalystand are normally carried out in an inert organic solvent.

[0006] U.S. Pat. No. 5,137,998 discloses a process for preparing arubbery terpolymer of styrene, isoprene, and butadiene having multipleglass transition temperatures and having an excellent combination ofproperties for use in making tire treads which comprises:terpolymerizing styrene, isoprene and 1,3-butadiene in an organicsolvent at a temperature of no more than about 40° C. in the presence of(a) at least one member selected from the group consisting oftripiperidino phosphine oxide and alkali metal alkoxides and (b) anorganolithium compound.

[0007] U.S. Pat. No. 5,047,483 discloses a pneumatic tire having anouter circumferential tread where said tread is a sulfur cured rubbercomposition comprised of, based on 100 parts by weight rubber (phr), (A)about 10 to about 90 parts by weight of a styrene, isoprene, butadieneterpolymer rubber (SIBR), and (B) about 70 to about 30 weight percent ofat least one of cis 1,4-polyisoprene rubber and cis 1,4-polybutadienerubber wherein said SIBR rubber is comprised of (1) about 10 to about 35weight percent bound styrene, (2) about 30 to about 50 weight percentbound isoprene and (3) about 30 to about 40 weight percent boundbutadiene and is characterized by having a single glass transitiontemperature (Tg) which is in the range of about −10° C. to about −40° C.and, further the said bound butadiene structure contains about 30 toabout 40 percent 1,2-vinyl units, the said bound isoprene structurecontains about 10 to about 30 percent 3,4-units, and the sum of thepercent 1,2-vinyl units of the bound butadiene and the percent 3,4-unitsof the bound isoprene is in the range of about 40 to about 70 percent.

[0008] U.S. Pat. No. 5,272,220 discloses a styrene-isoprene-butadienerubber which is particularly valuable for use in making truck tiretreads which exhibit improved rolling resistance and tread wearcharacteristics, said rubber being comprised of repeat units which arederived from about 5 weight percent to about 20 weight percent styrene,from about 7 weight percent to about 35 weight percent isoprene, andfrom about 55 weight percent to about 88 weight percent 1,3-butadiene,wherein the repeat units derived from styrene, isoprene and1,3-butadiene are in essentially random order, wherein from about 25% toabout 40% of the repeat units derived from the 1,3-butadiene are of thecis-microstructure, wherein from about 40% to about 60% of the repeatunits derived from the 1,3-butadiene are of the trans-microstructure,wherein from about 5% to about 25% of the repeat units derived from the1,3-butadiene are of the vinyl-microstructure, wherein from about 75% toabout 90% of the repeat units derived from the isoprene are of the1,4-microstructure, wherein from about 10% to about 25% of the repeatunits derived from the isoprene are of the 3,4-microstructure, whereinthe rubber has a glass transition temperature which is within the rangeof about −90° C. to about −70° C., wherein the rubber has a numberaverage molecular weight which is within the range of about 150,000 toabout 400,000, wherein the rubber has a weight average molecular weightof about 300,000 to about 800,000, and wherein the rubber has aninhomogeneity which is within the range of about 0.5 to about 1.5.

[0009] U.S. Pat. No. 5,239,009 reveals a process for preparing a rubberypolymer which comprises: (a) polymerizing a conjugated diene monomerwith a lithium initiator in the substantial absence of polar modifiersat a temperature which is within the range of about 5° C. to about 100°C. to produce a living polydiene segment having a number averagemolecular weight which is within the range of about 25,000 to about350,000; and (b) utilizing the living polydiene segment to initiate theterpolymerization of 1,3-butadiene, isoprene, and styrene, wherein theterpolymerization is conducted in the presence of at least one polarmodifier at a temperature which is within the range of about 5° C. toabout 70° C. to produce a final segment which is comprised of repeatunits which are derived from 1,3-butadiene, isoprene, and styrene,wherein the final segment has a number average molecular weight which iswithin the range of about 25,000 to about 350,000. The rubbery polymermade by this process is reported to be useful for improving the wet skidresistance and traction characteristics of tires without sacrificingtread wear or rolling resistance.

[0010] U.S. Pat. No. 5,061,765 discloses isoprene-butadiene copolymershaving high vinyl contents which can reportedly be employed in buildingtires which have improved traction, rolling resistance, and abrasionresistance. These high vinyl isoprene-butadiene rubbers are synthesizedby copolymerizing 1,3-butadiene monomer and isoprene monomer in anorganic solvent at a temperature which is within the range of about −10°C. to about 100° C. in the presence of a catalyst system which iscomprised of (a) an organoiron compound, (b) an organoaluminum compound,(c) a chelating aromatic amine, and (d) a protonic compound; wherein themolar ratio of the chelating amine to the organoiron compound is withinthe range of about 0.1:1 to about 1:1, wherein the molar ratio of theorganoaluminum compound to the organoiron compound is within the rangeof about 5:1 to about 200:1, and herein the molar ratio of the protoniccompound to the organoaluminum compound is within the range of about0.001:1 to about 0.2:1.

[0011] U.S. Pat. No. 5,405,927 discloses an isoprene-butadiene rubberwhich is particularly valuable for use in making truck tire treads, saidrubber being comprised of repeat units which are derived from about 20weight percent to about 50 weight percent isoprene and from about 50weight percent to about 80 weight percent 1,3-butadiene, wherein therepeat units derived from isoprene and 1,3-butadiene are in essentiallyrandom order, wherein from about 3% to about 10% of the repeat units insaid rubber are 1,2-polybutadiene units, wherein from about 50% to about70% of the repeat units in said rubber are 1,4-polybutadiene units,wherein from about 1% to about 4% of the repeat units in said rubber are3,4-polyisoprene units, wherein from about 25% to about 40% of therepeat units in the polymer are 1,4-polyisoprene units, wherein therubber has a glass transition temperature which is within the range ofabout −90° C. to about −75° C., and wherein the rubber has a Mooneyviscosity which is within the range of about 55 to about 140.

[0012] U.S. Pat. No. 5,654,384 discloses a process for preparing highvinyl polybutadiene rubber which comprises polymerizing 1,3-butadienemonomer with a lithium initiator at a temperature which is within therange of about 5° C. to about 100° C. in the presence of a sodiumalkoxide and a polar modifier, wherein the molar ratio of the sodiumalkoxide to the polar modifier is within the range of about 0.1:1 toabout 10:1; and wherein the molar ratio of the sodium alkoxide to thelithium initiator is within the range of about 0.05:1 to about 10:1. Byutilizing a combination of sodium alkoxide and a conventional polarmodifier, such as an amine or an ether, the rate of polymerizationinitiated with organolithium compounds can be greatly increased with theglass transition temperature of the polymer produced also beingsubstantially increased. The rubbers synthesized using such catalystsystems also exhibit excellent traction properties when compounded intotire tread formulations. This is attributable to the uniquemacrostructure (random branching) of the rubbers made with such catalystsystems.

[0013] U.S. Pat. No. 5,620,939, U.S. Pat. No. 5,627,237, and U.S. Pat.5,677,402 also disclose the use of sodium salts of saturated aliphaticalcohols as modifiers for lithium initiated solution polymerizations.Sodium t-amylate is a preferred sodium alkoxide by virtue of itsexceptional solubility in non-polar aliphatic hydrocarbon solvents, suchas hexane, which are employed as the medium for such solutionpolymerizations. However, using sodium t-amylate as the polymerizationmodifier in commercial operations where recycle is required can lead tocertain problems. These problems arise due to the fact that sodiumt-amylate reacts with water to form t-amyl alcohol during steamstripping in the polymer finishing step. Since t-amyl alcohol forms anazeotrope with hexane, it co-distills with hexane and thus contaminatesthe feed stream.

[0014] Tire rubbers which are prepared by anionic polymerization arefrequently coupled with a suitable coupling agent, such as a tin halide,to improve desired properties. Tin-coupled polymers are known to improvetreadwear and to reduce rolling resistance when used in tire treadrubbers. Such tin-coupled rubbery polymers are typically made bycoupling the rubbery polymer with a tin coupling agent at or near theend of the polymerization used in synthesizing the rubbery polymer. Inthe coupling process, live polymer chain ends react with the tincoupling agent thereby coupling the polymer. For instance, up to fourlive chain ends can react with tin tetrahalides, such as tintetrachloride, thereby coupling the polymer chains together.

[0015] The coupling efficiency of the tin coupling agent is dependant onmany factors, such as the quantity of live chain ends available forcoupling and the quantity and type of polar modifier, if any, employedin the polymerization. For instance, tin coupling agents are generallynot as effective in the presence of polar modifiers. However, polarmodifiers such as tetramethylethylenediamine, are frequently used toincrease the glass transition temperature of the rubber for improvedproperties, such as improved traction characteristics in tire treadcompounds. Coupling reactions that are carried out in the presence ofpolar modifiers typically have a coupling efficiency of about 50-60% inbatch processes. Lower coupling efficiencies are typically attained incontinuous processes.

[0016] U.S. Pat. No. application Ser. No. 09/461,653 discloses thatcoupling efficiency can be significantly improved by conducting thecoupling reactions in the presence of a lithium salt of a saturatedaliphatic alcohol, such as lithium t-amylate. In the alternativecoupling efficiency can also be improved by conducting the couplingreaction in the presence of a lithium halide, or a lithium phenoxide.U.S. patent application Ser. No. 09/461,653 specifically discloses aprocess for coupling a living rubbery polymer that comprises reactingthe living rubbery polymer with coupling agent selected from the groupconsisting of tin halides and silicon halides in the presence of alithium salt of a saturated aliphatic alcohol. The lithium salt of thesaturated aliphatic alcohol can be added immediately prior to thecoupling reaction or it can be present throughout the polymerization andcoupling process.

[0017] Each tin tetrahalide molecule or silicon tetrahalide molecule iscapable of reacting with up to four live polymer chain ends. However,since perfect stoichiometry is difficult to attain, some of the tinhalide molecules often react with less than four live polymer chainends. The classical problem is that if more than a stoichiometric amountof the tin halide coupling agent is employed, then there will be aninsufficient quantity of live polymer chain ends to totally react withthe tin halide molecules on a four-to-one basis. On the other hand, ifless than a stoichiometric amount of the tin halide coupling agent isadded, then there will be an excess of live polymer chain ends and someof the live chain ends will not be coupled. It is accordingly importantfor the stoichiometry to be exact and for all to the living polymerchain-ends to react with the coupling agent.

[0018] Conventional tin coupling results in the formation of a coupledpolymer that is essentially symmetrical. In other words, all of thepolymer arms on the coupled polymer are of essentially the same chainlength. All of the polymer arms in such conventional tin-coupledpolymers are accordingly of essentially the same molecular weight. Thisresults in such conventional tin-coupled polymers having a lowpolydispersity. For instance, conventional tin-coupled polymers normallyhaving a ratio of weight average molecular weight to number averagemolecular weight which is within the range of about 1.01 to about 1.1

[0019] U.S. Pat. No. 5,486,574 discloses dissimilar arm asymmetricradical or star block copolymers for adhesives and sealants. U.S. Pat.No. 5,096,973 discloses ABC block copolymers based on butadiene,isoprene and styrene and further discloses the possibility of branchingthese block copolymers with tetrahalides of silicon, germanium, tin orlead.

SUMMARY OF THE INVENTION

[0020] The tin coupling efficiency (degree of coupling) attained withliving polymers is normally reduced when polar modifiers, such astetramethylethylenediamine (TMEDA) are present. However, polar modifiersare needed to increase the glass transition temperature of rubberypolymers to obtain desired properties, such as improved tractioncharacteristics in tire tread compounds. Although a coupling efficiencywithin the range of 50 to 60 percent can be achieved in batch processesused in the synthesis of tin coupled styrene-butadiene rubbers, muchlower levels of coupling are realized in continuous processes.

[0021] It has been unexpectedly found that the coupling efficiency ofrubbery polymers made with polar modifiers can be significantly improvedby initiating the anionic polymerization with certain alkylsilyloxyprotected functional lithium initiators. In fact, coupling efficienciesof at least 70 percent are realized by utilizing the process of thepresent invention. In most, cases, coupling efficiencies of at least 80percent are realized by utilizing the process of the present invention.The alkylsilyloxy protected functional lithium initiators utilized inthe practice of this invention typically have a structural formulaselected from the group consisting of (a)

[0022] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein R representsalkyl groups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group containing from 1 to about 12 carbon atoms; (b)

[0023] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group containingfrom 1 to about 12 carbon atoms; and (c)

[0024] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms, and wherein A represents an alkylene group containing from 1 toabout 12 carbon atoms.

[0025] The present invention more specifically discloses a process forsynthesizing and coupling a rubbery polymer that comprises (1)polymerizing at least one conjugated diolefin monomer in the presence ofa polar modifier to produce a living rubbery polymer, wherein saidpolymerization is an anionic polymerization that is initiated with analkylsilyloxy protected functional lithium initiator having a thestructural formula selected from the group consisting of (a)

[0026] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein R representsalkyl groups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group containing from 1 to about 12 carbon atoms; (b)

[0027] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group containingfrom 1 to about 12 carbon atoms; and (c)

[0028] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms, and wherein A represents an alkylene group containing from 1 toabout 12 carbon atoms; and (2) reacting the living rubbery polymer witha coupling agent selected from the group consisting of tin halides andsilicon halides.

[0029] The present invention further discloses a process process forsynthesizing a rubbery polymer that comprises polymerizing at least oneconjugated diolefin monomer in the presence of a polar modifier toproduce a living rubbery polymer, wherein said polymerization is ananionic polymerization that is initiated with an alkylsilyloxy protectedfunctional lithium initiator having a the structural formula selectedfrom the group consisting of (a)

[0030] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein R representsalkyl groups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group that contains from 1 to about 12 carbon atoms; (b)

[0031] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group that containsfrom 1 to about 12 carbon atoms; and (c):

[0032] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms, and wherein A represents an alkylene group that contains from 1to about 12 carbon atoms.

[0033] The present invention also reveals a tire which is comprised of agenerally toroidal-shaped carcass with an outer circumferential tread,two spaced beads, at least one ply extending from bead to bead andsidewalls extending radially from and connecting said tread to saidbeads; wherein said tread is adapted to be ground-contacting; andwherein said tread is comprised of the carbon black, silica, and acoupled rubbery polymer made by a process that comprises (1)polymerizing at least one conjugated diolefin monomer in the presence ofa polar modifier to produce a living rubbery polymer, wherein saidpolymerization is an anionic polymerization that is initiated with analkylsilyloxy protected functional lithium initiator having a thestructural formula selected from the group consisting of (a)

[0034] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein R representsalkyl groups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group containing from 1 to about 12 carbon atoms; (b)

[0035] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group containingfrom 1 to about 12 carbon atoms; and (c)

[0036] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms, and wherein A represents an alkylene group containing from 1 toabout 12 carbon atoms; and (2) reacting the living rubbery polymer witha coupling agent selected from the group consisting of tin halides andsilicon halides.

[0037] The subject invention also reveals an initiator which isparticularly useful for initiating the anionic polymerization ofconjugated diolefin monomers into rubbery polymers said initiator havinga structural formula selected from the group consisting of (a)

[0038] wherein X represents a group IVa element selected from the groupconsisting of carbon, germanium, and tin, wherein R represents alkylgroups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group that contains from 1 to about 12 carbon atoms; (b)

[0039] wherein X represents a group IVa element selected from the groupconsisting of carbon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group that containsfrom 1 to about 12 carbon atoms; and (c):

[0040] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms, and wherein A represents an alkylene group that contains from 1to about 12 carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Virtually any type of rubbery polymer prepared by anionicpolymerization can be synthesized and coupled in accordance with thisinvention. The rubbery polymers that can be coupled will typically besynthesized by a solution polymerization technique that utilizes as theinitiator an alkylsilyloxy protected functional lithium initiator of thestructural formula: (a)

[0042] wherein X represents a group IVa element selected from the groupconsisting of carbon, germanium, and tin, wherein R represents alkylgroups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group that contains from 1 to about 12 carbon atoms; or (b)

[0043] wherein X represents a group IVa element selected from the groupconsisting of carbon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group that containsfrom 1 to about 12 carbon atoms; or (c)

[0044] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms, and wherein A represents an alkylene group that contains from 1to 12 carbon atoms. The alkylene group can be straight chained orbranched. For instance, A can represent a straight chained alkylenegroup of the structural formula —(CH₂)_(n)— or it can represent abranched alkylene group, such as:

[0045] wherein R represents alkyl groups that can be the same ordifferent, and wherein the alkyl groups contain from 1 to about 8 carbonatoms. R will typically represent an alkyl group containing from 1 toabout 4 carbon atoms. It is preferred for R to represent methyl groups.

[0046] The alkylsilyloxy protected functional lithium initiator can beof the structural formula:

[0047] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein n representsan integer from 1 to 10, wherein R represents alkyl groups that can bethe same or different, and wherein the alkyl groups contain from 1 toabout 8 carbon atoms, or an alkylsilyloxy protected functional lithiumcompound of the structural formula:

[0048] wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein n represents an integer from 1 to 10,wherein R represents alkyl groups that can be the same or different, andwherein the alkyl groups contain from 1 to about 8 carbon atoms. Theserubbery polymers will accordingly normally contain a “living” lithiumchain end.

[0049] The alkylsilyloxy protected functional lithium initiator can beof the structural formula:

[0050] wherein n represents an integer from 1 to 10, wherein Rrepresents alkyl groups that can be the same or different, and whereinthe alkyl groups contain from 1 to about 8 carbon atoms. It is normallypreferred for n to represent an integer from 1 to about 6. It is morepreferred from n to represent an integer from 2 to 4. It is typicallymost preferred from n to represent 3. In most cases, R will representalkyl groups containing from 1 to about 4 carbon atoms. R willpreferable represent methyl groups, ethyl groups, normal-propyl groups,or isopropyl groups. It is typically most preferred for R to representmethyl groups. A highly preferred initiator is3-(t-butyldimethylsilyloxy)-1-propyllithium which is commerciallyavailable from FMC Corporation.

[0051] The polymerizations employed in synthesizing the living rubberypolymers will normally be carried out in a hydrocarbon solvent. Suchhydrocarbon solvents are comprised of one or more aromatic, paraffinicor cycloparaffinic compounds. These solvents will normally contain fromabout 4 to about10 carbon atoms per molecule and will be liquid underthe conditions of the polymerization. Some representative examples ofsuitable organic solvents include pentane, isooctane, cyclohexane,methylcyclohexane, isohexane, n-heptane, n-octane, n-hexane, benzene,toluene, xylene, ethylbenzene, diethylbenzene, isobutylbenzene,petroleum ether, kerosene, petroleum spirits, petroleum naphtha, and thelike, alone or in admixture.

[0052] In the solution polymerization, there will normally be from 5 to30 weight percent monomers in the polymerization medium. Suchpolymerization media are, of course, comprised of the organic solventand monomers. In most cases, it will be preferred for the polymerizationmedium to contain from 10 to 25 weight percent monomers. It is generallymore preferred for the polymerization medium to contain 15 to 20 weightpercent monomers.

[0053] The polymerizations employed in making the rubbery polymer aretypically initiated by adding the alkylsiloxy protected functionalinitiator to an organic polymerization medium that contains themonomers. Such polymerizations are typically carried out utilizingcontinuous polymerization techniques. In such continuouspolymerizations, monomers and initiator are continuously added to theorganic polymerization medium with the rubbery polymer synthesized beingcontinuously withdrawn. Such continuous polymerizations are typicallyconducted in a multiple reactor system.

[0054] The rubbery polymers that are coupled in accordance with thisinvention can be made by the homopolymerization of a conjugated diolefinmonomer or by the random copolymerization of a conjugated diolefinmonomer with a vinyl aromatic monomer. It is, of course, also possibleto make living rubbery polymers that can be coupled by polymerizing amixture of conjugated diolefin monomers with one or more ethylenicallyunsaturated monomers, such as vinyl aromatic monomers. The conjugateddiolefin monomers which can be utilized in the synthesis of rubberypolymers which can be coupled in accordance with this inventiongenerally contain from 4 to 12 carbon atoms. Those containing from 4 to8 carbon atoms are generally preferred for commercial purposes. Forsimilar reasons, 1,3-butadiene and isoprene are the most commonlyutilized conjugated diolefin monomers. Some additional conjugateddiolefin monomers that can be utilized include2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, and the like, alone or in admixture.

[0055] Some representative examples of ethylenically unsaturatedmonomers that can potentially be synthesized into rubbery polymers whichcan be coupled in accordance with this invention include alkylacrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate,methyl methacrylate and the like; vinylidene monomers having one or moreterminal CH₂═CH— groups; vinyl aromatics such as styrene,α-methylstyrene, bromostyrene, chlorostyrene, fluorostyrene and thelike; α-olefins such as ethylene, propylene, 1-butene and the like;vinyl halides, such as vinylbromide, chloroethane (vinylchloride),vinylfluoride, vinyliodide, 1,2-dibromoethene, 1,1-dichloroethene(vinylidene chloride), 1,2-dichloroethene and the like; vinyl esters,such as vinyl acetate; α,β-olefinically unsaturated nitrites, such asacrylonitrile and methacrylonitrile; α,β-olefinically unsaturatedamides, such as acrylamide, N-methyl acrylamide, N,N-dimethylacrylamide,methacrylamide and the like.

[0056] Rubbery polymers which are copolymers of one or more dienemonomers with one or more other ethylenically unsaturated monomers willnormally contain from about 50 weight percent to about 99 weight percentconjugated diolefin monomers and from about 1 weight percent to about 50weight percent of the other ethylenically unsaturated monomers inaddition to the conjugated diolefin monomers. For example, copolymers ofconjugated diolefin monomers with vinylaromatic monomers, such asstyrene-butadiene rubbers which contain from 50 to 95 weight percentconjugated diolefin monomers and from 5 to 50 weight percentvinylaromatic monomers, are useful in many applications.

[0057] Vinyl aromatic monomers are probably the most important group ofethylenically unsaturated monomers which are commonly incorporated intopolydienes. Such vinyl aromatic monomers are, of course, selected so asto be copolymerizable with the conjugated diolefin monomers beingutilized. Generally, any vinyl aromatic monomer which is known topolymerize with organolithium initiators can be used. Such vinylaromatic monomers typically contain from 8 to 20 carbon atoms. Usually,the vinyl aromatic monomer will contain from 8 to 14 carbon atoms. Themost widely used vinyl aromatic monomer is styrene. Some examples ofvinyl aromatic monomers that can be utilized include styrene,1-vinylnaphthalene, 2-vinylnaphthalene, α-methylstyrene,4-phenylstyrene, 3-methylstyrene and the like.

[0058] Some representative examples of rubbery polymers which can becoupled in accordance with this invention include polybutadiene,polyisoprene, styrene-butadiene rubber (SBR), α-methylstyrene-butadienerubber, α-methylstyrene-isoprene rubber, styrene-isoprene-butadienerubber (SIBR), styrene-isoprene rubber (SIR), isoprene-butadiene rubber(IBR), α-methylstyrene-isoprene-butadiene rubber andα-methylstyrene-styrene-isoprene-butadiene rubber. In cases where therubbery polymer is comprised of repeat units that are derived from twoor more monomers, the repeat units which are derived from the differentmonomers will normally be distributed in an essentially random manner.

[0059] The amount of organolithium initiator utilized will vary with themonomers being polymerized and with the molecular weight that is desiredfor the polymer being synthesized. However, as a general rule, from 0.01to 1 phm (parts per 100 parts by weight of monomer) of an organolithiuminitiator will be utilized. In most cases, from 0.01 to 0.1 phm of anorganolithium initiator will be utilized with it being preferred toutilize 0.025 to 0.07 phm of the organolithium initiator.

[0060] The polymerization temperature utilized can vary over a broadrange of from about −20° C. to about 180° C. In most cases, apolymerization temperature within the range of about 30° C. to about125° C. will be utilized. It is typically preferred for thepolymerization temperature to be within the range of about 45° C. toabout 100° C. It is typically most preferred for the polymerizationtemperature to be within the range of about 60° C. to about 85° C. Thepressure used will normally be sufficient to maintain a substantiallyliquid phase under the conditions of the polymerization reaction.

[0061] The polymerization is conducted for a length of time sufficientto permit substantially complete polymerization of monomers. In otherwords, the polymerization is normally carried out until high conversionsare attained. The polymerization is then terminated by the addition of atin halide and/or silicon halide. The tin halide and/or the siliconhalide are continuous added in cases where asymmetrical coupling isdesired. This continuous addition of tin coupling agent and/or thesilicon coupling agent is normally done in a reaction zone separate fromthe zone where the bulk of the polymerization is occurring. In otherwords, the coupling will typically be added only after a high degree ofconversion has already been attained. For instance, the coupling agentwill normally be added only after a monomer conversion of greater thanabout 90 percent has been realized. It will typically be preferred forthe monomer conversion to reach at least about 95 percent before thecoupling agent is added. As a general rule, it is most preferred for themonomer conversion to exceed about 98 percent before the coupling agentis added. The coupling agents will normally be added in a separatereaction vessel after the desired degree of conversion has beenattained. The coupling agents can be added in a hydrocarbon solution,e.g., in cyclohexane, to the polymerization admixture with suitablemixing for distribution and reaction.

[0062] In cases where the rubbery polymer will be used in compounds thatare loaded primarily with carbon black, the coupling agent willtypically be a tin halide. The tin halide will normally be a tintetrahalide, such as tin tetrachloride, tin tetrabromide, tintetrafluoride or tin tetraiodide. However, tin trihalides can alsooptionally be used. Polymers coupled with tin trihalides having amaximum of three arms. This is, of course, in contrast to polymerscoupled with tin tetrahalides which have a maximum of four arms. Toinduce a higher level of branching, tin tetrahalides are normallypreferred. As a general rule, tin tetrachloride is most preferred.

[0063] In cases where the rubbery polymer will be used in compounds thatare loaded with high levels of silica, the coupling agent will typicallybe a silicon halide. The silicon coupling agents that can be used willnormally be silicon tetrahalides, such as silicon tetrachloride, silicontetrabromide, silicon tetrafluoride or silicon tetraiodide. However,silicon trihalides can also optionally be used. Polymers coupled withsilicon trihalides having a maximum of three arms. This is, of course,in contrast to polymers coupled with silicon tetrahalides which have amaximum of four arms. To induce a higher level of branching, silicontetrahalides are normally preferred. As a general rule, silicontetrachloride is most preferred of the silicon coupling agents.

[0064] Greatly improved properties for tire rubbers, such as lowerhysteresis, can be attained by coupling the rubber with both a tinhalide and a silicon halide. For instance, such coupled polymers can beutilized in making tires having greatly improved rolling resistancewithout sacrificing other tire properties. These improved properties aredue in part to better interaction and compatibility with carbon black.It is highly preferred for the polymer to be asymmetrically coupled witha tin halide and a silicon halide. Asymmetrical tin coupling alsonormally leads to improve the cold flow characteristics. Asymmetricalcoupling in general also leads to better processability and otherbeneficial properties. Rubbers that are coupled with both a tin halideand a silicon halide are comprised of (1) tin atoms having at leastthree polydiene arms covalently bonded thereto and (2) silicon atomshaving at least three polydiene arms covalently bonded thereto

[0065] This invention more specifically discloses a coupled rubberypolymer which is particularly valuable for use in manufacturing tiretread compounds, said coupled rubbery polymer being comprised of (1) tinatoms having at least three polydiene arms covalently bonded thereto and(2) silicon atoms having at least three polydiene arms covalently bondedthereto.

[0066] The tin coupling agent will normally be a tin tetrahalide, suchas tin tetrachloride, tin tetrabromide, tin tetrafluoride or tintetraiodide. However, tin trihalides can also optionally be used.Polymers coupled with tin trihalides having a maximum of three arms.This is, of course, in contrast to polymers coupled with tintetrahalides which have a maximum of four arms. To induce a higher levelof branching, tin tetrahalides are normally preferred. As a generalrule, tin tetrachloride is most preferred.

[0067] The silicon coupling agent will normally be a silicontetrahalide, such as silicon tetrachloride, silicon tetrabromide,silicon tetrafluoride or silicon tetraiodide. However, silicontrihalides can also optionally be used. Polymers coupled with silicontrihalides having a maximum of three arms. This is, of course, incontrast to polymers coupled with silicon tetrahalides which have amaximum of four arms. To induce a higher level of branching, silicontetrahalides are normally preferred. As a general rule, silicontetrachloride is most preferred.

[0068] The molar ratio of the tin halide to the silicon halide employedin coupling the rubbery polymer will normally be within the range of20:80 to 95:5. The molar ratio of the tin halide to the silicon halideemployed in coupling the rubbery polymer will more typically be withinthe range of 40:60 to 90:10. The molar ratio of the tin halide to thesilicon halide employed in coupling the rubbery polymer will preferablybe within the range of 60:40 to 85:15. The molar ratio of the tin halideto the silicon halide employed in coupling the rubbery polymer will mostpreferably be within the range of 65:35 to 80:20.

[0069] Asymmetrically rubbery polymers that are coupled with both tinand silicon contain stars of the structural formula:

[0070] wherein M represents silicon or tin, wherein R₁, R₂, R₃ and R4can be the same or different and are selected from the group consistingof alkyl groups and polydiene arms (polydiene rubber chains), with theproviso that at least three members selected from the group consistingof R₁, R₂, R₃ and R₄ are polydiene arms, with the proviso that at leastone member selected from the group consisting of R₁, R₂, R₃ and R₄ is alow molecular weight polydiene arm, with the proviso that at least onemember selected from the group consisting of R₁, R₂, R₃ and R₄ is a highmolecular weight polydiene arm, and with the proviso that the ratio ofthe weight average molecular weight to the number average molecularweight of the asymmetrical tin-coupled rubbery polymer is within therange of about 1.4 to about 2.5

[0071] In other words, asymmetrical rubbery polymers that are coupledwith both tin and silicon contain stars of the structural formulas:

[0072] wherein R¹, R², R³ and R⁴ can be the same or different and areselected from the group consisting of alkyl groups and polydiene arms(polydiene rubber chains), with the proviso that at least three membersselected from the group consisting of R¹, R², R³ and R⁴ are polydienearms. In most cases, four polydiene arms will be covalently bonded tothe tin atoms and the silicon atoms in the asymmetrical tin-coupledrubbery polymer. In such cases, R¹, R², R³ and R⁴ will all be polydienearms. It should be noted that R¹, R², R³ and R⁴ can be alkyl groupsbecause it is possible for the tin halide coupling agent to reactdirectly with alkyl lithium compounds which are used as thepolymerization initiator.

[0073] The polydiene arms in the asymmetrical tin-coupled rubberypolymers of this invention will typically have a weight averagemolecular weight that is within the range of about 80,000 to about300,000. The polydiene arms will more typically have a weight averagemolecular weight that is within the range of about 120,000 to about250,000. The ratio of the weight average molecular weight to the numberaverage molecular weight of the asymmetrical tin-coupled rubbery polymeris typically within the range of about 1.4 to about 2.5. The ratio ofthe weight average molecular weight to the number average molecularweight of the asymmetrical tin-coupled rubbery polymer is typicallywithin the range of about 1.4 to about 2.0. The ratio of the weightaverage molecular weight to the number average molecular weight of theasymmetrical tin-coupled rubbery polymer is more typically within therange of about 1.45 to about 1.8. The ratio of the weight averagemolecular weight to the number average molecalar weight of theasymmetrical coupled rubbery polymer is most typically within the rangeof about 1.5 to about 2.7. Normally at least one of the polydiene armscovalently bonded to the tin has a weight average molecular weight ofless than about 150,000 and at least one of the polydiene armscovalently bonded to the tin atom has a weight average molecular weightof greater than about 200,000.

[0074] The polydiene arms in the asymmetrical tin-coupled rubberypolymers of this invention are not block copolymers. In cases wherevinyl aromatic monomers, such as styrene, are present in the polydienearms they are not present in blocks containing more than about 4 repeatunits. In other words, the vinyl aromatic monomers will be distributedin a random fashion throughout the polydiene arms.

[0075] Optionally, silicon trialkyl halide or a tin trialkyl halide,such as tin tributyl chloride, can be used to functionalize all or aprotion of the rubbery polymer. For instance, the living rubbery polymercan be coupled and functionalized by utilizing a combination of silicontetrachloride and tin tributylchloride.

[0076] Broadly, and exemplary, a range of about 0.01 to 4.5milliequivalents of tin coupling agent (tin halide and silicon halide)is employed per 100 grams of the rubbery polymer. It is normallypreferred to utilize about 0.01 to about 1.5 milliequivalents of thecoupling agent per 100 grams of polymer to obtain the desired Mooneyviscosity. The larger quantities tend to result in production ofpolymers containing terminally reactive groups or insufficient coupling.One equivalent of tin coupling agent per equivalent of lithium isconsidered an optimum amount for maximum branching. For instance, if amixture tin tetrahalide and silicon tetrahalide is used as the couplingagent, one mole of the coupling agent would be utilized per four molesof live lithium ends. In cases where a mixture of tin trihalide andsilicon trihalide is used as the coupling agent, one mole of thecoupling agent will optimally be utilized for every three moles of livelithium ends. The coupling agent can be added in a hydrocarbon solution,e.g., in cyclohexane, to the polymerization admixture in the reactorwith suitable mixing for distribution and reaction.

[0077] After the coupling has been completed, a tertiary chelating alkyl1,2-ethylene diamine or a metal salt of a cyclic alcohol can optionallybe added to the polymer cement to stabilize the coupled rubbery polymer.The tertiary chelating amines that can be used are normally chelatingalkyl diamines of the structural formula:

[0078] wherein n represents an integer from 1 to about 6, wherein Arepresents an alkylene group containing from 1 to about 6 carbon atomsand wherein R′, R″, R′″ and R″″ can be the same or different andrepresent alkyl groups containing from 1 to about 6 carbon atoms. Thealkylene group A is of the formula —(—CH₂—)_(m) wherein m is an integerfrom 1 to about 6. The alkylene group will typically contain from 1 to 4carbon atoms (m will be 1 to 4) and will preferably contain 2 carbonatoms. In most cases, n will be an integer from 1 to about 3 with itbeing preferred for n to be 1. It is preferred for R′, R″, R′″ and R″″to represent alkyl groups which contain from 1 to 3 carbon atoms. Inmost cases, R′, R′″, R′″ and R″″ will represent methyl groups.

[0079] In most cases, from about 0.01 phr (parts by weight per 100 partsby weight of dry rubber) to about 2 phr of the chelating alkyl1,2-ethylene diamine or metal salt of the cyclic alcohol will be addedto the polymer cement to stabilize the rubbery polymer. Typically, fromabout 0.05 phr to about 1 phr of the chelating alkyl 1,2-ethylenediamine or metal salt of the cyclic alcohol will be added. Moretypically, from about 0.1 phr to about 0.6 phr of the chelating alkyl1,2-ethylene diamine or the metal salt of the cyclic alcohol will beadded to the polymer cement to stabilize the rubbery polymer.

[0080] After the polymerization, coupling, and optionally thestabilization step, has been completed, the coupled rubbery polymer canbe recovered from the organic solvent. The coupled rubbery polymer canbe recovered from the organic solvent and residue by means such asdecantation, filtration, centrification and the like. It is oftendesirable to precipitate the coupled rubbery polymer from the organicsolvent by the addition of lower alcohols containing from about 1 toabout 4 carbon atoms to the polymer solution. Suitable lower alcoholsfor precipitation of the rubber from the polymer cement includemethanol, ethanol, isopropyl alcohol, normal-propyl alcohol and t-butylalcohol. The utilization of lower alcohols to precipitate theasymmetrically tin-coupled rubbery polymer from the polymer cement also“kills” any remaining living polymer by inactivating lithium end groups.After the coupled rubbery polymer is recovered from the solution,steam-stripping can be employed to reduce the level of volatile organiccompounds in the coupled rubbery polymer.

[0081] This invention is illustrated by the following examples which aremerely for the purpose of illustration and are not to be regarded aslimiting the scope of the invention or the manner in which it can bepracticed. Unless specifically indicated otherwise, all parts andpercentages are given by weight.

EXAMPLE 1

[0082] In this experiment, a tin coupled styrene-butadiene rubber wasprepared at 70° C. In the procedure used, 2300 g of asilica/alumina/molecular sieve dried premix containing 19.5 weightpercent styrene/1,3-butadiene mixture in hexanes was charged into aone-gallon (3.8 liters) reactor. The ratio of styrene to 1,3-butadienewas 15:85. After the amount of impurity in the premix was determined,2.4 ml of 1M solution of TMEDA (N, N, N′, N′-tetramethylethylene-diaminein hexanes), and 4.3 ml. of 0.7M solution of3-(t-butyldimethylsilyloxy)-1-propyllithium (in cyclohexane) were addedto the reactor. The target Mn (number averaged molecular weight) was150,000. The polymerization was allowed to proceed at 70° C. for 1.5hours. The GC analysis of the residual monomers contained in thepolymerization mixture indicated that most of the monomers wereconverted to polymer. After a small aliquot of polymer cement wasremoved from the reactor (for analysis), 1.2 ml. of a 0.6M solution oftin tetrachloride (in hexanes) was added to the reactor and the couplingreaction was carried out the same temperature for an hour. At this time,1.0 phr (parts per 100 parts of rubber by weight) of BHT(2,6-di-tert-butyl-4-methylphenol) and 3.0 ml of 1M solution of TMEDAwere added to the reactor to shortstop the polymerization and tostabilized the polymer. After evaporating the hexanes, the resultingpolymer was dried in a vacuum oven at 50° C. The coupledstyrene-butadiene rubber (SBR) produced was determined to have a glasstransition temperature (Tg) at −45° C. It was also determined to have amicrostructure, which contained 49 percent 1,2-polybutadiene units, 37percent 1,4-polybutadiene units and 14 percent random polystyrene units.The Mooney viscosity (ML-4) at 100° C. for this coupled polymer was alsodetermined to be 114. The ML-4 for the base polymer (before coupling)was 25. Based on GPC measurement, the coupling efficiency was 83%.

COMPARATIVE EXAMPLE 2

[0083] The procedure described in Example 1 was utilized in this exampleexcept that 2.92 ml of 1M solution of n-butyllithium (in hexanes) wasused as the polymerization initiator. The Tg and microstructure of theresulting coupled SBR are shown in Table 1. The Mooney viscosities ofthe base and coupled polymers are also shown in Table 1. The couplingefficiency was 55%, based on GPC measurement. TABLE 1 Exam- Tg ML-4Microstructure (%) Coupling ple (° C.) Base Coupled 1,2-PBd 1,4-PBdStyrene Efficiency 1 −44 25 114 49 37 14 83% 2 −45 25 85 49 37 14 55

EXAMPLE 3

[0084] The tin coupled SBR prepared in this experiment was synthesizedin a three-reactor (1 gallon, 2 gallon, 2 gallon) continuous system at80° C. A premix containing styrene and 1,3-butadiene in hexanes wascharged into the first polymerization reactor continuously at a rate of98 grams per minute. The premix monomer solution containing a ratio ofstyrene to 1,3-butadiene of 18:82 and had a total monomer concentrationof 16%. Polymerization was initiated by adding3-(t-butyl-dimethylsilyloxy)-1-propyl lithium (0.6 mmole/100 grams ofmonomer) and TMEDA (1 mmole/100 grams monomer) to the first reactorcontinuously. The resulting polymerization medium containing the liveends was continuously pushed to the second rector (for completing thepolymerization) and then the third reactor where the coupling agent, tintetrachloride, (0.15 mmole/100 grams monomer) was added continuously.The residence time for all reactors was set at one hour to achievecomplete monomer conversion in the second reactor and complete couplingat the third reactor. The polymerization medium was continuously pushedover to a holding tank containing stabilizer and antioxidant. Theresulting polymer cement was then steam stripped and the recovered SBRwas dried in a vented oven at 50° C. The polymer was determined to havea glass transition temperature at −43° C. and have a Mooney ML-4viscosity of 80. The Mooney viscosity of base (uncoupled precursor) was32. It was also determined to have a microstructure, which contained 18%random polystyrene units, 41% 1,2-polybutadiene units, and 41%1,4-polybutdiene units.

EXAMPLE 4

[0085] The produce described in Example 3 was utilized in this exampleexcept that n-butyllithium was used as the initiator. The Tg andmicrostructure of the resulting coupled SBR are shown in Table 2. TheMooney viscosities of the base and coupled polymers are also shown inTable 2. TABLE 2 Tg ML-4 Microstructure (%) Example (° C.) Base Coupled1,2-PBd 1,4-PBd Styrene 3 −43 32 80 41 41 18 4 −42 42 68 42 41 17

EXAMPLE 5

[0086] In this example, a 50/50 isoprene-butadiene rubber (IBR)containing a silyloxyl functional group was prepared. In the procedureused, 2300 g of a silica/alumina/molecular sieve dried premix containing19.0 weight percent isoprene/1,3-butadiene mixture in hexanes wascharged into a one-gallon (3.8 liters) reactor. The ratio of styrene to1,3-butadiene was 50:50. After the amount of impurity in the premix wasdetermined, 1.7 ml of 1M solution of TMEDA(N,N,N′,N′-tetramethylethylene-diamine in hexanes), and 2.5 ml. of 0.7Msolution of 3-(t-butyldimethylsilyloxy)-1-propyllithium (in cyclohexane)were added to the reactor. The target Mn (number averaged molecularweight) was 250,000. The polymerization was allowed to proceed at 70° C.for 2.5 hours. The GC analysis of the residual monomers contained in thepolymerization mixture indicated that most of the monomers wereconverted to polymer. At this time, the polymerization mixture wasshortstopped with 2.0 ml. of 1M ethanol solution (in hexanes). Theresulting polymer was stabilized with 1.0 phr (parts per 100 parts ofrubber by weight) of BHT (2,6-di-tert-butyl-4-methylphenol). Afterevaporating the hexanes, the resulting polymer was dried in a vacuumoven at 50° C. The IBR produced was determined to have a glasstransition temperature (Tg) at −45° C. It was also determined to have amicrostructure, which contained 24 percent 1,2-polybutadiene units, 26percent 1,4-polybutadiene units, 22 percent 1,4-polyisoprene units, 27percent 3,4-polyisoprene units and 1% 1,2-polyisoprene unit. The Mooneyviscosity (ML-4) at 100° C. for this polymer was also determined to be65.

EXAMPLE 6

[0087] In this example, a telechelic 50/50 isoprene-butadiene rubbercontaining a silyloxyl functional group at the beginning of the polymerchain and an alkoxysilyl functional group at the end of polymer chainwas prepared. The procedure described in Example 5 was used in thisexample except that 3-chloropropyltriethoxysilane was added to thepolymerization mixture at the completion of polymerization (2.5 hours)to form an ethoxysilyl end functionalized IBR. The telichelic IBRproduced was determined to have a glass transition temperature (Tg) at−44° C. It was also determined to have a microstructure which contained25 percent 1,2-polybutadiene units, 25 percent 1,4 -polybutadiene units,22 percent 1,4-polyisoprene units, 27 percent 3,4-polyisoprene units and1% 1,2-polyisoprene unit. The Mooney viscosity (ML-4) at 100° C. forthis polymer was also determined to be 69.

EXAMPLE 7

[0088] In this example, a telechelic 50/50 isoprene-butadiene rubbercontaining a silyloxy functional group at the beginning of the polymerchain and a alkoxysilyl sulfane functional group at the end of polymerchain was prepared. The procedure described in Example 5 was used inthis example except that bis(3-triethoxylsilylpropyl)disulfane was usedin place of 3-chloropropyltriethoxy-silane to functionalize the polymerchain ends. The resulting telichelic IBR produced was determined to havea glass transition temperature (Tg) a −45° C. It was also determined tohave a microstructure which contained 24 percent 1,2-polybutadieneunits, 26 percent 1,4-polybutadiene units, 22 percent 1,4-polyisopreneunits, 22 percent 3,4-polyisoprene units and 2% 1,2-polyisoprene unit.The Mooney viscosity (ML-4) at 100° C. for this polymer was alsodetermined to be 72.

EXAMPLE 8

[0089] In this example, a 30/70 styrene-butadiene rubber (SBR)containing a silyloxy functional group was prepared. The proceduredescribed in Example 5 was utilized in this example except that amixture of styrene and 1,3-butadiene in hexanes was used as themonomers. The ratio of styrene to 1,3-butadiene was 30:70. The silyloxyfunctionalized SBR produced was determined to have a glass transitiontemperature (Tg) at −29° C. It was also determined to have amicrostructure which contained 41 percent 1,2-polybutadiene units, 31percent 1,4-polybutadiene units and 28 percent random polystyrene units.The Mooney viscosity (ML-4) at 100° C. for this polymer was alsodetermined to be 70.

EXAMPLE 9

[0090] In this example, a telechelic 30/70 styrene-butadiene rubbercontaining a silyloxy functional group at the beginning of the polymerchain and an alkoxysilyl functional group at the end of polymer chainwas prepared. The procedure described in Example 6 was utilized in thisexample except that a mixture of styrene and 1,3-butadiene in hexaneswas used as the monomers. The ratio of styrene to 1,3-butadiene was30:70. The telichelic SBR produced was determined to have a glasstransition temperature (Tg) at −30° C. It was also determined to have amicrostructure which contained 40 percent 1,2-polybutadiene units, 31percent 1,4-polybutadiene units and 29 percent random polystyrene units.The Mooney viscosity (ML-4) at 100° C. for this polymer was alsodetermined to be 73.

EXAMPLE 10

[0091] In this example, a telechelic 30/70 styrene-butadiene rubbercontaining a silyloxy functional group at the beginning of the polymerchain and a alkoxysilyl sulfane functional group at the end of polymerchain was prepared. The procedure described in Example 7 was utilized inthis example except that a mixture of styrene and 1,3-butadiene inhexanes was used as the monomers. The ratio of styrene to 1,3-butadienewas 30:70. The telichelic SBR produced was determined to have a glasstransition temperature (Tg) at −29° C. It was also determined to have amicrostructure which contained 39 percent 1,2-polybutadiene units, 32percent 1,4-polybutadiene units and 29 percent random polystyrene units.The Mooney viscosity (ML-4) at 100° C. for this polymer was alsodetermined to be 89.

COMPARATIVE EXAMPLE 11

[0092] A 15/85 SBR was prepared, using a standard anionic polymerizationtechnique, in a one gallon batch reactor with a TMEDA modifiedn-butyllithium (n-BuLi)catalyst at 70° C. The TMEDA/n-BuLi molar ratiowas 0.85/1. It took 90 minutes to complete the polymerization. Tintetrachloride in hexane (0.25/1 molar ratio to n-BuLi) was then added tothe resulting polymer cement. The coupling reaction was carried out at atemperature of 70° C. for 30 minutes. The polymer was then stabilizedwith TMEDA/BHT. The coupling efficiency, the Tg, and the Mooney ML-4viscosity of the polymer are listed in Table 3.

EXAMPLE 12

[0093] The procedure described in Example 11 was repeated in thisexample except that 3-(tributyltin)-1-propyllithium (Bu₃Sn(CH₂)₃Li),provided by Chemetall-Foote Co. was used as the initiator. The couplingefficiency, the glass transition temperature, and the Mooney ML-4viscosity of the tin functionalized-coupled polymer are also listed inTable 3. TABLE 3 Example Tg Base ML-4 Coupled ML-4 % Coupling* 11 44° C.33  99 55 12 46° C. 34 120 79

[0094] While certain representative embodiments and details have beenshown for the purpose of illustrating the subject invention, it will beapparent to those skilled in this art that various changes andmodifications can be made therein without departing from the scope ofthe subject invention.

What is claimed is:
 1. A process for synthesizing and coupling a rubberypolymer that comprises (1) polymerizing at least one conjugated diolefinmonomer in the presence of a polar modifier to produce a living rubberypolymer, wherein said polymerization is an anionic polymerization thatis initiated with an alkylsilyloxy protected functional lithiuminitiator having a the structural formula selected from the groupconsisting of (a):

wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein R representsalkyl groups that can be the same or different, wherein the alkyl groupscontain from 1 to about 8 carbon atoms, and wherein A represents analkylene group containing from 1 to about 12 carbon atoms; (b):

wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein R represents alkyl groups that can bethe same or different, wherein the alkyl groups contain from 1 to about8 carbon atoms, and wherein A represents an alkylene group containingfrom 1 to about 12 carbon atoms; and (c):

wherein R represents alkyl groups that can be the same or different, andwherein the alkyl groups contain from 1 to about 8 carbon atoms, andwherein A represents an alkylene group containing from 1 to about 12carbon atoms; and (2) reacting the living rubbery polymer with both atin halide and a silicon halide.
 2. A process as specified in claim 1wherein A represents a branched alkylene group having the structuralformula:

wherein R represents methyl groups.
 3. A process as specified in claim 1wherein said process is conducted in the presence of a polar modifier.4. A process as specified in claim 3 wherein said polar modifier isselected from the group consisting of diethyl ether, di-n-propyl ether,diisopropyl ether, di-n-butyl ether, tetrahydrofuran, dioxane, ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycoldimethyl ether, diethylene glycol diethyl ether, triethylene glycoldimethyl ether, trimethylamine, triethylamine,N,N,N′,N′-tetramethylethylenediamine, N-methyl morpholine, N-ethylmorpholine, N-phenyl morpholine, and alkyltetrahydrofurfuryl ethers. 5.A process as specified in claim 1 wherein the alkylsilyloxy protectedfunctional lithium initiator is3-(t-butyldimethylsilyloxy)-1-propyllithium.
 6. A process as specifiedin claim 1 wherein the conjugated diolefin monomer is 1,3-butadiene andwherein the rubbery polymer is polybutadiene rubber.
 7. A process asspecified in claim 1 wherein the tin halide is a tin tetrahalide andwherein the silicon halide is a silicon tetrahalide.
 8. A process asspecified in claim 1 wherein the tin halide is a tin trihalide andwherein the silicon halide is a silicon trihalide.
 9. A process asspecified in claim 7 wherein the tin tetrahalide is tin tetrachlorideand wherein the silicon tetrahalide is silicon tetrachloride.
 10. Aprocess as specified in claim 1 which farther comprises copolymerizingstyrene monomer with the conjugated diolefin monomer, wherein theconjugated diolefin monomer is 1,3-butadiene and wherein the rubberypolymer is styrene-butadiene rubber.
 11. A process as specified in claim1 wherein the polar modifier is N,N,N′,N′-tetramethylethylenediamine.12. A process as specified in claim 1 wherein the alkylsilyloxyprotected functional lithium initiator has a the structural formulaselected from the group consisting of (a):

wherein X represents a group IVA element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein n representsan integer from 1 to 10, wherein R represents alkyl groups that can bethe same or different, and wherein the alkyl groups contain from 1 toabout 8 carbon atoms, and (b):

wherein X represents a group IVa element selected from the groupconsisting of carbon, silicon, germanium, and tin, wherein Y representsphosphorous or nitrogen, wherein n represents an integer from 1 to 10,wherein R represents alkyl groups that can be the same or different, andwherein the alkyl groups contain from 1 to about 8 carbon atoms.
 13. Aprocess as specified in claim 1 wherein the alkylsilyloxy protectedfunctional lithium initiator is of the structural formula:

wherein n represents an integer from 1 to 10, wherein R represents alkylgroups that can be the same or different, and wherein the alkyl groupscontain from 1 to about 8 carbon atoms.
 14. A process as specified inclaim 13 wherein n represents an integer from 2 to 4, and wherein Rrepresents an alkyl group containing from 1 to about 4 carbon atoms. 15.A process as specified in claim 13 wherein n represents 3 and wherein Rrepresents methyl groups.
 16. A rubbery polymer made by the processspecified in claim
 1. 17. A rubber compound which is comprised of therubbery polymer specified in claim 16, carbon black, and silica.
 18. Atire which is comprised of a generally toroidal-shaped carcass with anouter circumferential tread, two spaced beads, at least one plyextending from bead to bead and sidewalls extending radially from andconnecting said tread to said beads; wherein said tread is adapted to beground-contacting; and wherein said tread is comprised of the rubbercompound specified in claim 17.